The present invention relates generally to a protective barrier for a fuel cell stack health monitoring system, and more particularly to an environmental barrier which protects the receiver portion of a fuel cell stack health monitoring system.
In a typical fuel cell system, hydrogen or a hydrogen-rich gas is supplied as a reactant through a flowpath to the anode side of a fuel cell while oxygen (such as in the form of atmospheric oxygen) is supplied as a reactant through a separate flowpath to the cathode side of the fuel cell. Catalysts, typically in the form of a noble metal such as platinum, are placed at the anode and cathode to facilitate the electrochemical conversion of the reactants into electrons and positively charged ions (for the hydrogen) and negatively charged ions (for the oxygen). An electrolyte layer separates the anode from the cathode to allow the selective passage of ions from the anode to the cathode while simultaneously prohibiting the passage of the generated electrons, which instead are forced to flow through an external electrically-conductive circuit (such as a load) to perform useful work before recombining with the charged ions at the cathode. The combination of the positively and negatively charged ions at the cathode results in the production of non-polluting water as a byproduct of the reaction.
One form of fuel cell, called the proton exchange membrane (PEM) fuel cell, has shown particular promise for vehicular and related mobile applications. The electrolyte layer of a PEM fuel cell is in the form of a solid proton-transmissive membrane (such as a perfluorosulfonic acid membrane, a commercial example of which is Nafion™). The presence of an anode separated from a cathode by such an electrolyte layer forms a single PEM fuel cell; many such single cells can be combined to form a fuel cell stack, increasing the power output thereof. Multiple stacks can be coupled together to further increase power output.
Fuel cells require balanced water levels to ensure proper operation. For example, it is important to avoid having too much water in the fuel cell, which can result in the flooding or related blockage of the reactant flowfield channels, thereby hampering cell operation. On the other hand, too little hydration limits the electrical conductivity of the membrane and can lead to premature cell failure. Exacerbating the difficulty in maintaining a balance in water level is that there are numerous conflicting reactions taking place in a fuel cell that are simultaneously increasing and decreasing local and global hydration levels.
Regarding flooding in particular, as more flow channels are blocked and less reactant gas flows through, electricity produced by the fuel cell decreases. Because the fuel cells are electrically coupled in series, if one of the fuel cells fails, the entire stack may fail. For this reason, determining the presence or absence of liquid water in a fuel cell flowfield is desirable. However, the hydration and water level balance requirements of the fuel cell create a less-than-ideal environment for the electronics used to sense and determine such water presence. Current systems for monitoring fuel cell stack health include wired transmission of stack vitals. However, the wired transmission equipment is particularly susceptible to humidity and the presence of liquid water.